Technical Field
The present invention relates to a tsunami breakwater wall of retaining wall structure supported by steel pipe piles and its construction method. In particular, the invention relates to a tsunami breakwater wall of retaining wall structure supported by steel pipe piles and its construction method that is advantageous in withstanding tsunamis and earthquakes and effective for providing measures against tsunamis at areas such as seashores and seaports.
Related Art
The off the Pacific coast of Tohoku earthquake (the huge earthquake that occurred with the epicenter off the Sanriku Pacific Coast on Mar. 11, 2011) had brought damages due to the tsunami creating the need for immediate provision of tsunami-resistant facilities such as a tsunami breakwater and the like at the seashore, seaports and the like. Various facilities have already been built in these areas and are used for navigation of ships, cargo work, freight transport complex and the like and therefore, tsunami-resistant facilities such as tsunami breakwaters need to be built taking such circumstances into consideration.
Japanese Patent Application Laid-open Publication No. 5-44206 (PTL 1) describes an example of a breakwater. This breakwater is constructed by forming a mound by spreading crushed stone and the like over the ground of the seabed, installing bearing piles into this mound while allowing the upper portions of the bearing piles to protrude upward from the mound, loading concrete caissons on the mound and engaging the upper portions of the bearing piles to the energy absorbing material inside the depression provided to the bottom of the caissons.
According to the breakwater described in PTL 1, when an external force such as wave power and the like is applied to the breakwater, the energy acting on breakwater can be relieved by the energy absorbing material deforming due to the external force and absorbing the energy of the external force, thus allowing to alleviate the inclination and subsidence of the caisson on the mound thereby significantly improving the durability of the breakwater.
And another example of a breakwater is described in Japanese Patent Application Laid-open Publication No. 10-252036 (PTL 2). This breakwater has piles installed with intervals therebetween to form a retarding chamber in the sea at the front of the breakwater wall, a perforated plate vertically attached to these piles, and the piles and the perforated plate connected with a support rod to the front part of the breakwater.
The perforated plate includes a perforated plate main body composed of an approximately rectangular concrete planar member provided with thick protruding portions at the rear right and left parts thereof, and the perforated plate is vertically attached to the piles by inserting the piles into the penetration holes of these thick protruding portions. Further, a plurality of oblong holes is made in the vertical direction with intervals therebetween at the center of the front face of the perforated plate.
According to the breakwater described in PTL 2, improvement work of existing breakwaters can be performed without affecting existing breakwaters since the perforated plate and the breakwaters are configured independent of each other and the perforated plate is configured to be supported by being attached to the piles installed to the seabed.
Japanese Patent Application Laid-open Publication No. 2001-3331 (PTL 3) describes further another example of a breakwater. This breakwater includes a plurality of piles installed in two rows so that the head portions protrude from the surface of the seabed, a curtain wall is integrally provided to the row of piles on the off shore side and orthogonal to the direction in which the waves move, and a connecting block that is provided to integrate the top portions of the four piles.
The aforementioned curtain wall is formed by combining a plurality of approximately T-shape wave-dissipating blocks. Further, each of the wave-dissipating blocks has provided thereto a penetration hole that vertically penetrates each wave-dissipating block. And a wave-dissipating block and a pile are integrated by inserting the pile into this penetration hole.
According to the breakwater described in PTL 3, a curtain wall composed of a plurality of wave-dissipating blocks supported by a row of piles on the off shore side can be constructed by inserting each of the piles of the row of piles on the off shore side into the penetration holes of each of the wave-dissipating blocks. Additionally, the row of piles on the off shore side and the row of piles on the shore side can be integrated by integrating with a connection block the top portions of four piles of the row of piles on the off shore side and the row of piles on the shore side. Accordingly, the construction performance can be improved and thus allowing the construction cost to be reduced.